remove hhvm testing

travis-ci records this error:

Using worker: worker-linux-7-1.bb.travis-ci.org:travis-linux-9
git.1
$ git clone --depth=50 --branch=develop-2 git://github.com/auraphp/Aura.Di.git auraphp/Aura.Di
Cloning into 'auraphp/Aura.Di'...
remote: Counting objects: 1028, done.
remote: Compressing objects: 100% (471/471), done.
remote: Total 1028 (delta 530), reused 957 (delta 461)
Receiving objects: 100% (1028/1028), 183.78 KiB, done.
Resolving deltas: 100% (530/530), done.
$ cd auraphp/Aura.Di
git.3
$ git checkout -qf e5e06e0d867f1843c2e0f7c861ad7843fba2f6f1
$ phpenv global hhvm
$ php --version
HipHop VM v2.3.0 (rel)
Compiler: heads/HHVM-2.3-0-ga12fa4ac4dacbb45348a6ff2b3775f895883f934
Repo schema: 30349d0b2f68667d4e5a3fd291f2274c608f9e29
$ composer --version
Cannot open log file: /var/log/hhvm/error.log
HipHop Strict Warning: It is not safe to rely on the system's timezone settings. Please use the date.timezone setting, the TZ environment variable or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'UTC' for 'UTC/0.0/no DST' instead in phar://composer.phar/bin/../src/../src/Composer/Console/Application.php on line 65
Composer version 80499bb02418711b34bba59c1a6d8032429e5702 2013-12-06 12:32:19
before_script
$ cd tests
$ phpunit
Cannot open log file: /var/log/hhvm/error.log
PHPUnit 3.7.28 by Sebastian Bergmann.
Configuration read from /home/travis/build/auraphp/Aura.Di/tests/phpunit.xml
..F................................
Time: 1.17 seconds, Memory: 5.08Mb
There was 1 failure:
1) Aura\Di\ConfigTest::testFetchCapturesParentParams
Failed asserting that Array (
    'foo' => null
    'zim' => null
) is identical to Array (
    'foo' => 'bar'
    'zim' => null
).
phar://phpunit-3.7.28.phar/phpunit/Framework/Constraint.php:147
phar://phpunit-3.7.28.phar/phpunit/Framework/Constraint/IsIdentical.php:132
phar://phpunit-3.7.28.phar/phpunit/Framework/Assert.php:2134
phar://phpunit-3.7.28.phar/phpunit/Framework/Assert.php:1095
/home/travis/build/auraphp/Aura.Di/tests/src/ConfigTest.php:42
phar://phpunit-3.7.28.phar/phpunit/Framework/TestCase.php:983
phar://phpunit-3.7.28.phar/phpunit/Framework/TestCase.php:838
phar://phpunit-3.7.28.phar/phpunit/Framework/TestResult.php:648
phar://phpunit-3.7.28.phar/phpunit/Framework/TestCase.php:783
phar://phpunit-3.7.28.phar/phpunit/Framework/TestSuite.php:775
phar://phpunit-3.7.28.phar/phpunit/Framework/TestSuite.php:745
phar://phpunit-3.7.28.phar/phpunit/Framework/TestSuite.php:705
phar://phpunit-3.7.28.phar/phpunit/TextUI/TestRunner.php:349
phar://phpunit-3.7.28.phar/phpunit/TextUI/Command.php:176
phar://phpunit-3.7.28.phar/phpunit/TextUI/Command.php:129
FAILURES!
Tests: 35, Assertions: 59, Failures: 1.
The command "phpunit" exited with 1.
Done. Your build exited with 1.